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Old 05-19-2011, 11:26 AM   #1
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Air sealing attic


The home is a split level built in 1965 in Ottawa, Canada.

I am planning on air sealing the attic and adding some extra insulation and baffles between the rafters for ventilation.
I've already cutout some extra vents in the plywood soffits and installed these soffit covers I got from HD.


The existing attic insulation is black paper backed (tar product??) fiberglass that is stapled to the joists, therefore no poly VB.

What I plan on doing is:
- Air sealing around any electrical boxes
- Spray foaming (with Great Stuff) the tops of any top plates on interior walls. If I can get to them, I plan on spray foaming the exterior wall top plates too...however its a low pitch roof (see picture) and I think it will be difficult.
- air sealing around the plumbing stack.
- air sealing around any dropped soffits (only 1)


My questions:
1) Should I un-staple the existing paper backed insulation to get to the interior wall partition top plates? I'm not sure I'd be able to re-staple it because its old insulation and its hard to un-staple without tearing.

2) Which way should the fins of the soffit covers point? From the picture I attached it looks like they're pointing TOWARDS to house. I would have thought that they point AWAY from the house.


I've also attached a picture of the house I'll be working on. Notice the low pitch roof. Since the roof is low pitched, installing attic baffles is more than a challenge and since I'm not planning on removing the ceilings from the rooms below, anyone have experience with getting in tight places near where the rafters meet the exterior wall?

thanks,
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Old 05-19-2011, 01:17 PM   #2
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Air sealing attic


I think your approach is ok. Does the house have a ridge vent or gable ends? Hard to tell from the picture. If yes on the ridge, you should have the whole soffit ventilated as much as possible. Don't have a guideline for how many vents per foot off the top of my head but if you had siding on there and you were going to cover up the soffit with trim, I would tell you to vent the length of the run on each side. Doing so now would require you to find a continuous vent like 30 feet long (or whatever it is) but that probably is not strictly necessary. Also, you could close up the gable end vents if there is a ridge vent. If no ridge vent, then leave the gable ends alone. It is not ideal but getting a ridge vent in place would be a next step.

IMO, any old insulation should just be chucked and replaced with new stuff. For true air sealing, you will need to expose the whole attic floor (not necessarily all at once if you are doing this as a DIY) so that you can get to every significant crack where all drywall/walls meet. Same with plumbing runs, junction boxes, etc.

In my home, the pitch of the roof is fairly low. Don't have a number for you but I am 6'1" and about 160. I could barely fit in the cavities plus I had to lay on a board of plywood. Lots of reaching and hitting my head on the roof deck. What a pita! Blood was shed on that job. If you are a big guy, either lose some weight or get a punk kid in there : - )

Also, consider sealing the outside wall perimeter/ceiling joint in the attic. Yes, this is at the absolute tightest reach on your home. It will suck. I had good sized open joints. I used silicone caulk because it was hard to reach a spray foam can there. I had to use latex gloves to spread the caulk around in the gap. Spray foam would work ok but you need to plan ahead if you are using the cans. Those cans are a one time shot and the best I could ever do was get two uses out of them. Just remember, moving from one joist cavity to another is not instantaneous. Factor that time in as well. After placing in the air baffles, I also blocked/supported the baffles with both fiberglass batting and foamed in rigid foam (a bit overkill here). You have to allow for air to get into the attic but you can direct it so that it does not wash down the exterior walls. Hence the reason why I said you should seal up the outer perimeter wall/ceiling gap (if it exists on your home).

One last thing, any caulk or spray foam you use should be done with a cleaned surface. You will need a vacuum up there to make that happen.

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Old 05-19-2011, 02:21 PM   #3
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Air sealing attic


Thanks for the reply!

Quote:
Originally Posted by algored2deth View Post
Does the house have a ridge vent or gable ends?
It has a 10 ft ridge vent in the middle of the roof as well as 2 gable end vents. I am planning on adding 2 Maxi roof vents (popular here in Canada what with high snow levels on our roofs). The soffits are ventilated every 6 or 7 feet and covered with the grill (I included a picture in my first post). I will one day remove the entire soffit board when I install aluminum fascia on the eaves but that isn't in the near future ($$ constraints). For the meantime, I have cut openings in the soffits and installed more soffit covers. I currently have soffit vents every 4 ft and I am doubling the size of the opening and covering it with 2 covers put together.


Quote:
Originally Posted by algored2deth View Post
Also, consider sealing the outside wall perimeter/ceiling joint in the attic.
I just found an interesting idea on how to do it on these forums: caulk in a piece of XPS foam between the ceiling joists that cover the exterior top plate. The only problem will be getting them in there since the roof is low pitched.
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Old 05-19-2011, 10:11 PM   #4
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Air sealing attic


i have a couple pics to show what i did. might be in a couple replies.
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Old 05-19-2011, 10:13 PM   #5
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second pic. this is where i put FG batt underneath chute for some support and air blockage.
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Old 05-19-2011, 10:15 PM   #6
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pic three. this is where i went a little overkill with rigid foam. works for me. doing the work was ugly but i will never have to go up there again. i had cellulose put on top of all of the existing insulation.
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Old 05-20-2011, 09:48 AM   #7
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Wow great pics and thanks for sharing....yup, looks like I have a little less room at the eaves than you do.
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Old 05-22-2011, 01:11 AM   #8
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Be sure to use the foam board over the plate as close to the outside as possible. Fiberglass is the worst for stopping air, great for an air filter, though. With the outside air saturating the fiberglass on the cold side of the foam board and insulated attic, you will have basically zero R-value over the plate not covered by f.b. The good news is the heat lost from the wall cavity by conduction or convective loops there will be rapidly lost without depositing additional moisture in the attic. The "biggest loser" in fiberglass insulation....

The louvers should face outward so as not the draw the rain/snow in the wind pressure coming up the side of the house from below, install them close to the fascia, if possible; pp.616: http://books.google.com/books?id=Z8a...0vents&f=false

Low slope insulating: http://www.homeenergy.org/archive/he...96/961110.html

Tearing the asphalt paper still leaves it effective as a vapor barrier (which you want), not an air barrier. Air seal everywhere first, as mentioned: http://oee.nrcan.gc.ca/residential/p...ap4.cfm?attr=4

The louver/screened rectangular vents lose NFVA on the dimensional size: http://www.lomanco.com/intakemain.html

The math: http://www.airvent.com/homeowner/pro...it-specs.shtml

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Old 05-24-2011, 01:32 PM   #9
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So the image in the first post installing the vent is wrong? The louvers should go the other way?
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Old 05-24-2011, 11:29 PM   #10
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Yep, wrong…

“Locate the soffit vent next to the fascia board. The closer the vent is located to the exterior wall, the closer it gets to the area of positive wind pressure. This increases the chance of rain or snow penetration.
Avoid single-louvered soffit vents. There are two ways to install them, one of which is wrong. Eliminating them gets rid of the worry of whether they were correctly installed, and possible lawsuits from water damage.
Use only a double-louvered soffit vent. It cannot be installed backwards. The louvers face in opposite directions (Fig.23-10, which helps create a turbulence that helps keep snow from entering the attic space.” From: http://books.google.com/books?id=Z8a...0vents&f=false


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Old 05-25-2011, 06:31 AM   #11
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You are like some kind of sick attic god.

Great information only problem I have is trying to remember where all the links are I save from your posts.
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Old 05-25-2011, 08:31 AM   #12
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Quote:
Originally Posted by GBR in WA View Post
Be sure to use the foam board over the plate as close to the outside as possible. Fiberglass is the worst for stopping air, great for an air filter, though. With the outside air saturating the fiberglass on the cold side of the foam board and insulated attic, you will have basically zero R-value over the plate not covered by f.b. The good news is the heat lost from the wall cavity by conduction or convective loops there will be rapidly lost without depositing additional moisture in the attic.

I actually do agree with using the extra rigid board, provided you can get to it. Even though my pics show what seems to be all kinds of space available, it was a tight fit. I believe I had 42 rafter/joist cavities to fill. It was a lot of work doing what I did and seemingly never ending. Putting in the extra work may have paid off but at the same time, I am ok with the end results. I have no ice damming and it is better than it was. Cutting out another 42 pics of rigid foam is just a pain. Each cavity is slightly different and fitting it becomes just more frustrating. Believe me, I was not a nice person while working on this project.

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